This invention relates to an automatic pistol adaptable to fire cartridges of different calibers. More specifically, this invention relates to an automatic pistol of the breech block type interconvertible to fire cartridges of different calibers.
The conversion of breech block types of automatic pistols such as the Colt Government Model .45 to a subcaliber has usually resulted in a permanent alteration to the sub-caliber. Such conversions have generally utilized the grip or frame end, in some cases, the firing mechanism of the larger caliber pistol, but have required a new slide, extractor and ejector as well as a new barrel and magazine, or permanent alterations to an existing slide, ejector and extractor.
The barrel in a Colt .45 is connected to the frame by a pivotal link and is interlocked to the slide by ribs as well as by tension from a recoil spring mounted in the slide. Upon recoil, the barrel and slide move backwardly together for a short distance. Because of its pivotal linkage to the frame, the rear part of the barrel moves downwardly, disengaging from the slide and allowing the slide to continue its rearward movement. The backward movement of the slide causes the firing mechanism to be cocked and causes the extraction and ejection of the cartridge case. At the end of the backward movement of the slide, the compressed recoil spring moves the slide forward causing a cartridge to be withdrawn from the magazine and pushed into the chamber of the barrel in firing position. Near the end of its forward movement the slide again engages the barrel and the pivotal movement is reversed causing the barrel and slide to interengage.
Previous modifications such as disclosed by Williams, U.S. Pat. No. 2,090,657, alter this form of operation. The subcaliber barrel, instead of being reciprocable, is rigidly secured to the frame. In many conversion kits the new slide is fixedly secured to the barrel, and the rear portion of the slide, referred to as the breech block, retreats to eject an empty case, cock the pistol and returns to firing position, thus loading the firing chamber with a fresh cartridge. These modifications do not contain a locked breech. Without a breechlock the action often starts opening before the bullet is out of the barrel greatly affecting the accuracy of the firearm. Typical conversions are to be found in U.S. Pat. No. 2,872,850; U.S. Pat. No. 2,898,693 and U.S. Pat. No. 3,724,326.
One reason given by gunsmiths for requiring a new slide, or permanent alteration to an existing slide, for sub-caliber conversion is that, due to the great difference in case head size, such as between a 0.45 and 0.38, the slide will not work well with the sub-caliber cartridges. Presumably, this is due to the extractor and the cartridge locating recess in the breechface of the slide being specific to one case head diameter only.
Prior art extractors have been constructed in such a manner that the movement allowed for capturing and extracting a cartridge case has been within very specific dimensional tolerances. If an extractor projects too far into the breech toward the center of the bore, it may interfere with the cartridge during feeding or loading causing the breech block to malfunction or jam. On the other hand, if an extractor rests too far away from the center line of the bore it will fail to interface with the cartridge case head or rim and fail to capture and extract the cartridge case from the firing chamber.
It is also the prevailing opinion of many skilled in the art that a new slide, having a sub-caliber cartridge locating recess, or an existing slide, permanently altered, by reducing the size of the cartridge locating recess (by either "welding-up" and remachining, or permanently installing a bushing) is necessary to prevent the sub-caliber cartridge from becoming dislocated in the breech thus avoiding capture and extraction.